1. Field of the Invention
The present invention relates to a seed crystal fixing apparatus for fixing a seed crystal to a seed crystal setting part of a reaction vessel with interposition of an adhesive, and a method for fixing the seed crystal.
2. Related Art
Silicon carbides have larger band gap and more excellent in dielectric breakdown property, heat resistance, radiation resistance and the like as compared with silicon, therefore, have been noticed as electronic device materials such as portable and high output semiconductors and the like, and due to excellent optical properties, noticed as optical device materials. Among such silicon carbide crystals, silicon carbide single crystals have a merit that they are particularly excellent in uniformity of properties in wafer when applied to devices such as wafers and the like as compared with silicon carbide polycrystals.
As a method of producing the above-mentioned silicon carbide single crystal, Improved Rayleigh method (improved sublimation re-crystallization method) is known in which a graphite crucible is used, a silicon carbide powder is sublimated and a silicon carbide single crystal is grown on a seed crystal of a silicon carbide single crystal.
When the seed crystal is grown without being completely bonded to the seed crystal setting part in improved Lely method, macroscopic defects (void defects) penetrate through the seed crystal from the side of the seed crystal setting part where the seed crystal is not completely bonded into the growing crystal, and the quality of the wafer was liable to be impaired. Since the adhesive is gasified at high temperatures, it has been also conjectured that remaining bubbles of the gasified adhesive in the adhesive layer causes deterioration of the quality of the crystal.
Several techniques have been proposed for solving the above-mentioned problems (for example. see Japanese Patent Application Laid-Open Nos. 2001-139394 and 2003-119098). Japanese Patent Application Laid-Open No. 2001-139394 discloses, for example, a method for fixing the seed crystal by applying a given pressure. Japanese Patent Application Laid-Open No. 2003-119098 discloses a fixing method for press-bonding the seed crystal by mounting a weight on the seed crystal.
However, it was difficult to uniformly bond the entire surface of the seed crystal by the mechanical press-bond method which cause the surface of the seed crystal finely roughened. Uniform press-bonding with a weight was also difficult.